The increasing size of wind turbines and trend towards offshore turbines puts high demands on serviceability and robustness that the current rolling element bearing systems cannot provide. Also, due to fact that large wind turbines have large dynamic shaft deflections, high loads and low speeds makes it difficult for plain bearings to work and last in the demanded lifetime.
Conventional wind turbine designs use conventional roller bearings or ball bearings for carrying the drive train, the generator on direct drive turbines and hub with blades require. When such conventional roller bearings or ball bearings have to be replaced, for example at the end of their life cycle, this can be performed only by disassembling the drive train, the generator and/or the hub with blade. These operations require the use of a costly crane capacity. Such costs are especially high for wind turbines located offshore, for which a jackup vessel has to be used.
One solution to the above problem is the use of fluid bearings instead of roller bearings or ball bearings.
Another solution to the above problem is to enhance the serviceability of the roller bearings or ball bearings to a higher level. In particular, it is known that the structural integrity of ball or roller bearings is significantly compromised by any axial movement caused by axial thrust forces.
Therefore, serviceability of the roller bearings or ball bearings may be improved by completely or at least in part by absorbing such axial thrust forces.
In addition, it is further important in wind turbines to know the value of such axial thrust force. Measurement of the thrust force on the wind turbine rotor provides a significant amount of information about the operational state of the turbine. The information can be used by the control system to reduce loading on main components e.g. tower, blades etc.
A common way of measuring the rotor thrust is by measuring the strain in the individual blade roots and transforming the measurement to collective rotor thrust. The strain measurement is typically performed using strain gauges or most recently fiber Bragg sensors. Another method is measuring strain on a main support structure on the turbine e.g. the main shaft.
The main issue with these approaches it that strain gauges need maintenance during the lifetime and for complex structures like the main shaft of a direct drive turbine the strain distribution is complex making the placement of the strain gauges and strain to thrust transformations a critical problem.
It is a purpose of embodiments of the present invention to provide a thrust bearing for a wind turbine, which absorbs the axial thrust forces, acting on ball or roller or fluid bearings, in order to enhance the serviceability of the wind turbine. It is desirable that the thrust bearing itself provides an enhanced level of serviceability by allowing easy maintenance and replacement of the thrust bearing.
It is a further purpose of embodiments of the present invention to provide a thrust bearing for a wind turbine, which allows a simple robust and cheap method for measuring the thrust force acting on the thrust bearing.